1. Field of the Invention
The present invention relates generally to base cards for use in manufacturing semiconductor chip cards and to the semiconductor chip cards themselves. More particularly, the present invention relates to a base card which overcomes problems which have in the past arisen when mounting a Chip on Board (COB) package into the base card in the manufacture of a chip card.
2. Description of the Related Art
To address the simultaneous and competing demands for high numbers of input/output (I/O) pins and miniaturization of the semiconductor device packages, a new packaging technology has been proposed in which a semiconductor device is directly mounted on a printed circuit board (PCB) without constructing a package assembly using a lead frame. Such a semiconductor device package is referred to as a COB (Chip On Board) package.
Memory cards have become the prominent high capacity memory media in current use. They have been developed for storing and/or recording captions, sounds, and stationary video images of electronic entertainment machines and of digital still cameras. Memory cards have also been developed as substitutes for hard disks of computers, and for use in portable information storage and retrieval machines. Such memory cards, in general, are manufactured by packaging a number of memory chips into a single base card.
Memory cards may include miniature cards, compact flash cards and smart card media. Among these, miniature cards and compact flash cards have disadvantages of high cost and bulkiness because they must have a built-in controller.
IC cards such as SmartMedia or SSFDC (Solid State Floppy Disc Cards) are used for storing digital signals and contain a COB package having a built-in memory chip. These IC cards are advantageous over the conventional memory cards in that they are smaller, have a high extensibility due to the identical pin numbers between generations, and are very portable. SmartMedia is a new small card for recording or storing captions, sounds or stationary video images generated by digital entertainment machines or portable computers. SmartMedia is also used in an embedded or removed state for storing information of digital still cameras. Moreover, SmartMedia is expected to be extensively used for a wide range of applications since it has a greater capacity than diskettes or ID cards using magnetic tape, and is easy to store and handle.
All IC cards should have means which allow them to be electrically connected to external appliances. The cards should also have standardized means which allow them to be freely attached to or detached from appliances, such as digital still cameras, produced by different manufacturers in the same way that floppy disks can be used with various makes of computers.
A chip card is produced by mounting a COB package containing a semiconductor chip to a standardized base card. The base card is used for ease in handling and for aiding an electrical connection between the COB package and the external appliances. This is because the size of the COB package makes it difficult to handle and because it is difficult or impossible to electrically connect the COB package itself to external electronic appliances such as digital still cameras.
The conventional base card and the chip card using it will be described with reference to FIGS. 1 to 3. FIG. 1 is an exploded perspective view of a COB package mounted to a conventional base card; FIG. 2 is a cross-sectional view taken along line 2--2 in FIG. 1; and FIG. 3 is a perspective view of a conventional chip card.
With reference to FIGS. 1 to 3, the conventional chip card 100 consists of a COB package 20, to which a semiconductor chip 40 is mounted, and a base card 10 for receiving the package 20.
The COB package 20 comprises a semiconductor chip 40, a printed circuit board 23, bonding wires 29 and package body 24. The chip 40 is attached to a chip bonding area 21 of the upper surface of the printed circuit board 23, and the chip 40 is electrically connected to circuit patterns 26 by bonding wires 29 made of gold (Au) or aluminum (Al). External connection means 27 are formed on the bottom surface of the board 20 and are electrically connected to the circuit patterns 26 by way of via holes 28, the inner walls of which are plated with an electrically conductive material. Thus, the circuit patterns 26, which are electrically connected to the chip 40 by the bonding wires 29, are also electrically connected to the external connection means 27 by way of the via holes 28. The upper surface of the printed circuit board 23 is molded with a thermosetting compound (`molding compound`), such as an epoxy resin, to form the package body 24. This package body 24 protects the chip 40 from external stresses. Molding dams 22 may be formed on the printed circuit board 23 to prevent the molding compound from flowing out during the molding process. Therefore, the molding dams 22 surround the package body 24.
The base card 10 has a receiving part 13 which has a shape complementary with and for receiving the package body 24 of the COB package. The receiving part 13 is usually formed at the middle of the base card and has a downwardly stepped configuration. The receiving part 13 has two sections: a first section 12 which receives the periphery of the COB package, and a second section 14 which extends downward from the first section 12 and receives the package body 24.
The mounting of the COB package 20 to the base card 10 will be described hereinafter. An adhesion means 30, such as adhesive tape, is placed on the bottom of the first section 12 of the receiving part 13. The COB package 20 is aligned with the receiving part 13, and the package body 24 of COB package 20 is fit into the second section 14 of the receiving part 13 while the periphery of the printed circuit board 23 is fit into the first section 12 of the receiving part 13. Then, the periphery of the printed circuit board 23 is pressed while supplying heat thereto by using, for example, a thermo-press machine (not shown). This completes the attaching of the COB package to base card 10. Note that the adhesive tape 30 has an opening 32 through which the second section 14 of the receiving part 13 is exposed.
Accordingly, the conventional chip card 100 has a structure in which the external connection means 27 of the COB package 20 is exposed and used for the electrical connection of the card 100 to external electronic appliances such as digital still cameras.
The structure of the chip card 100 will described in more detail hereinafter. Since the chip card 100 is manufactured by assembling a standardized base card 10 and standardized COB package 20 together, the thickness of the base card 10 when added to that of the package 20 must be uniform. In general, referring to FIG. 2, the thickness (c) of the package 20 is 640 .mu.m.-+.50 .mu.m, the overall thickness (a) of the card 10 is 810 .mu.m.-+.20 .mu.m, and the thickness (b) of the bottom of the second section 14 of the receiving part 13 is 140 .mu.m.-+.20 .mu.m. Because the thickness (b) of the second section 14 is less than the overall thickness (a) of base card 10, it is difficult to achieve uniformity in the thickness of the chip card 100 along the bottom of the second section 14 of the receiving part 13.
The manufacturing process of the base card will be described with reference to FIG. 4. The mold 60 used for manufacturing the base card consists of upper 63 and lower 65 mold dies, which when fit together form a cavity 61 which has the same configuration as that of the base card. A fluid molding compound 70 is introduced into the cavity 61 to form a molded base card article. The base card has different thicknesses; the periphery has the greatest thickness, the first section of the receiving part has an intermediate thickness, and the central second section of the receiving part has the smallest thickness. Therefore, the flow rate of the fluid molding compound becomes greatest at the bottom of the second section of the receiving part, possibly resulting in an incomplete molding at this location.
The incomplete molding may produce unevenness or voids in the bottom of the second section 14 of the receiving part 13. The latter may cause the second section of the receiving part to break after the COB package is mounted on the base card.
Moreover, the COB packages may contain by-products 25 produced during the molding process (`molding by-products`), such as epoxy burrs or molding flashes, since they are molded onto a PCB by using a fluid molding compound. Thus, with reference to FIG. 5, a mounting failure can occur due to a molding by-product 25 formed on the outside of the package body 24 of the COB package when the COB package is mounted to the receiving part 13 of the base card 10.
Furthermore, as mentioned above, the COB package 20 is manufactured by encapsulating the chip 40 on the printed circuit board 23. In this case, the printed circuit board 23 may have dams (22 in FIG. 1) at its periphery surrounding the chip 40 to prevent the flowing out of fluid molding compound used to form the encapsulant. However, the dams are not as rigid as the dam bars of a conventional lead frame package. Accordingly, a larger amount of molding by-products 25 are formed than when the package is molded using a lead frame. Moreover, it is difficult to remove the by-products 25 from the COB package since the by-products 25 are present on the surface thereof where the circuit patterns are formed. Specifically, any chemical or mechanical deflash process to remove the by-products may damage the circuit patterns or the printed circuit board itself. On the other hand, deflash and dam-bar trimming procedures can easily be used to remove the by-products of a molding process from a package having a conventional lead frame without damage to the lead frame or circuit board.
In addition, the gate into which the fluid molding compound is introduced or the air vents through which the air communicates may be degraded by large molding by-products 25 such as epoxy burrs having a thickness of, for example, 0.5 mm or more.
When the COB package 20 having the molding by-products 25 is placed on and mounted to the base card 10, the by-products 25 will be located at the edges where the inclined surface 16 of the receiving part 13 is in contact with the bottom of the first section 12 thereof, resulting in a mismatch between the package 20 and the base card 10 as shown in FIG. 5.
Moreover, when there is a mismatch between the COB package 20 and the base card 10, the pressure applied to the COB package 20 to attach it to the receiving part 13 of the base card will concentrate at the bottom of the second section 14 of the receiving part 13, resulting in the failure of the base card 10 at the bottom of the second section 14 of the receiving part 13.